1. Field of the Invention
The present invention is in the field of grinding devices, and more particularly devices for grinding various solid materials such as sand, coal, ores or the like which are randomly sized within certain ranges when received and must be reduced to a predetermined smaller size range for further processing.
2. The Prior Art
As is well known, it is frequently necessary to grind solid particulate matter, such as sand, ores, etc. as an interim step in the utilization of such material. The grinding is typically effected in mills, such as ball or rod mills.
It is, of course, desirable to utilize the milling capacity in an efficient manner, whereby the maximum through-put of material milled to the desired size range is achieved.
In milling systems heretofore known, various means have been proposed to optimize efficiency. In virtually all such systems, materials are continuously introduced into the mill and at the same time increments of milled materials extracted. The extracted materials may include increments reduced to the desired range and further increments which, while larger than desired, are nonetheless smaller than the raw particulate starting material.
In accordance with known practice, the material which has been subjected to the milling operation is classified, as by known air classifiers or the like, the suitably sized finished product or "fines" being removed and the partially ground material reintroduced to the mill along with increments of raw materials.
The proportioning of raw material to partially ground material has been found significantly to affect milling efficiency and various automatic proportioning means have been suggested. In accordance with one such system, microphones are employed as sensors to determine by the nature of the sounds emitted in the mill, the time, amount and proportion in which additional materials are to be fed to and extracted from the mill.
Various other types of controls relying upon differential air pressures, photoelectric apparatus and like feed rate sensors have been suggested for controlling the milling procedure. By way of example, attention is directed to U.S. Pat. Nos. 1141,898; 2480,998; 3179,345; 3690,570 and 3779,469.
It will be readily recognized that the noted systems are, by and large, extremely expensive to install and maintain, are complex in their operation and, where variations in conditions (i.e. where the raw materials differs in particle size from typical, or where the apparatus it utilized to process a different material, for example from ore to sand) are experienced, the readjustment and resetting of the control mechanisms to accommodate the new conditions is laborious and requires substantial expertise.
Notwithstanding the existence of a multiplicity of automatic control systems, proportioning of ingredients in the majority of milling operations is today manually controlled, and the efficiency of the system is in large measure dependent upon the skill and experience of the operator.